The Development of a Detailed Abundance Analysis Method Intended for the Integrated Light Spectra of Extragalactic Globular Clusters.

Abstract

Globular clusters are stellar systems that possess an astrophysically rare combination of theoretical and observational simplicity, which make them ideal diagnostic tracers of astrophysical processes in both space and time. Capitalizing on this simplicity, this dissertation develops and demonstrates a detailed abundance analysis method that is capable of computing all observable line abundances (i.e. Fe‐ peak elements, alpha‐elements, neutron‐capture elements, and light‐elements) from the integrated light spectra of extragalactic globular clusters (GCs). The premise behind the method is that the precise and accurate techniques used for single star abundance analysis can be combined with theoretical simple stellar population (SSP) models to synthesize light‐weighted absorption line equivalent widths (EWs). By iterating on the assumed abundance for a line until its synthesized EW equals its observed EW allows its line abundance to be determined. The development and demonstration of this method is carried out using a training set of seven Milky Way GCs (NGC 104, NGC 362, NGC 2808, NGC 6093, NGC 6388, NGC 6397, NGC 6752), which were observed using a spectrograph scanning technique that produces integrated light spectra that mimic extragalactic GC spectra. The role of the training set is two fold. First, because the training set clusters are spatially resolved, their stellar populations are known a priori in the form of color‐magnitude diagrams. The use of these known stellar populations in the analysis method serve to initially test the feasibility of the method without encountering any of the potential complications that may stem from using theoretical SSPs. Second, because the clusters are spatially resolved, their stellar abundances are known a priori from single star abundance analysis. These stellar abundances critically serve as fiducial abundances against which the dissertation's abundance results are tested. The major conclusion from this dissertation is that its abundance analysis method using theoretical SSPs is capable of deriving the detailed abundances of extragalactic GCs with an accuracy and precision that are competitive with standard stellar abundance analysis. The method produces abundances that are on average only < 0.1 dex larger than the abundances from stellar analysis, and their statistical uncertainties are on average ~ 0.2 dex.